The present invention relates generally to semiconductor memory devices, and more particularly to dynamic random access memories (DRAM) and a method for controlling DRAMs.
As the technology and speed of processors such as microprocessors and other computer controllers continue to improve, the need for fast and efficient memory devices increases. Often, processors are limited by the speed at which they can retrieve needed data from memory devices. If the data is not available when the processor needs it, the processor stalls until the data is available. This slows the throughput of the system. Consequently, improvements to currently available memory devices are needed to meet the demands of future processors.
Currently available commercial memory devices, such as DRAMs, typically read and write data over a data bus through a bi-directional I/O port. One measure of the efficiency of a memory system is the percentage of time that the data bus is being used. It is desirable that the data bus usage be kept high, so that as much data as possible can be transferred in a given amount of time. If the data bus usage percentage is low, the cycles in which no data is transferred are lost. The lost cycles are cumulative, and for long data transfers result in the loss of a significant amount of bandwidth on the data bus.
Another factor in determining the efficiency of a memory system is the amount of latency in the system. Latency is the time between the receipt of a read or write instruction and the beginning of data transfer on the data bus. Latency can add delay to the time between when data is requested and when it is received. However, if efficiently managed, this small delay at the beginning of a data transfer becomes insignificant overall.
It is desirable to provide a memory device that operates efficiently. Preferably, the memory device will operate to maximize the overall efficiency of the memory system by making optimum usage of the data bus. Consequently, an improved memory device method of operation of a memory device is needed.